This invention concerns a system to roll at least two sections in blocks of fast rolling mill stands.
The blocks of fast rolling mill stands according to the invention in a rolling plant are located downstream of a train of conventional rolling mill stands and upstream of a cooling line comprising a cooling plate.
The invention is applied to the situation where rolled products sheared to size are obtained on the cooling plate.
The rolling mill stands with which the invention is concerned are called commercially "blocks of fast rolling mill stands" and consist typically of a plurality of alternate pairs of rolls positioned as cantilevers with their axes rotated by ninety degrees to the next pair so as to process, for instance, oval sections followed by round sections followed by oval sections followed by round sections and so on.
These fast rolling mill stands can roll at 60 to 80 meters per second or more up to 120 to 140 meters per second.
In the blocks of fast rolling mill stands with which the invention is concerned the distance between the centre of one pair of rolling rolls and the centre of the next pair of rolling rolls is generally between 600 to 1200 millimeters.
It is known that the rolled product leaving the fast rolling mill stands undergoes an in-line cooling process carried out by feeding the rolled product into a cooling station consisting of cooling plates after the rolled product has been sheared to size.
It is also known that the maximum speed which can be reached in the entry channel of a cooling plate is about 20 to 30 meters per second in the double channels but more usually 12 to 20 meters per second in the roller conveyors owing to reasons linked to the handling and discharge of the bars of rolled stock.
Owing to the above the advantages connected to the use of these blocks of fast rolling mill stands are therefore substantially lessened, because also of the fact that these blocks of the state of the art can be employed only to roll one profile at a time.
The state of the art includes the so-called "splitting process" to increase the speed of processing of the rolled stock, this process consisting in processing at the same time two or more sections obtained by splitting a double initial rolled product.
In the state of the art this process has never been employed in fast rolling mill stand blocks owing to the difficulties linked to the rotation of the rolling plane from the horizontal to the vertical where there are successive pairs of rolls, close together as in this case, with alternate horizontal/vertical axes.
In fact, in passing from a module having a vertical axis to a module having a horizontal axis it is necessary to bring the two sections from a position superimposed on each other in a vertical plane to a position side by side on a horizontal plane while keeping constant the axial positioning of the single sections in relation to the horizontal.
Another problem encountered in employing these blocks of fast rolling mill stands in methods of rolling two sections relates to the bending of the axis of the cantilever rolls during the rolling step.
In fact, these cantilever rolls in blocks of fast rolling mill stands have a diameter of a rather small size of about 160 to 250 millimeters and are borne on shafts of a consequently very small diameter.
The problem of the bending of the shafts and of the geometric alteration of the reciprocal positions of the rolls when one single section is being rolled is important but can now be deemed to have been overcome in the state of the art.
But a problem which has still not been overcome is the simultaneous rolling of two substantially equal sections arranged side by side inasmuch as, if the distance between center of the two sections exceeds a given minimum value, a bending of the rolls takes place which changes substantially the geometric working conditions as between one section and the other.
Yet another unsolved problem, as we said, concerns the rotation of the plane of positioning of the two sections in the limited space between one pair of rolls and the next pair.
Still another problem is the lead-in equipment which guides the sections into the inlet of a pair of rolls and which requires minimum safety dimensions so as not to become worn and break quickly.